大断面富水岩溶隧道二次衬砌受力特征研究

Study on Mechanical Characteristics of Secondary Lining for Large Cross-section Tunnel in Water-rich Karst Strata

基于重庆双碑隧道现场测试并采用FLAC^(3D)进行数值模拟,研究富水岩溶地层大断面隧道二次衬砌力学行为。现场测试表明:二衬在混凝土硬化前逐步受力,二次衬砌轴力始终为压力,拱顶承受正弯矩,拱腰边墙承受负弯矩,安全系数拱顶大于边墙;当衬砌背后存在外水压时,外水压对衬砌的环箍效应明显。数值模拟表明:轴力、弯矩随水压增加呈线性增长,轴力下半断面测点不仅数值上高于上半断面而且增长速度也明显高于上半断面,弯矩增长速度拱脚>仰拱>上半断面;当隧道排水能力足够时,排导式衬砌结构基本不承担外水压力,一旦排水能力下降,在外水压力作用下结构的承载能力较弱,拱脚及仰拱为危险区域,极可能产生结构压裂、突水等滞后型危害。

In order to explore the mechanical behavior of secondary lining of large section tunnel in water-rich karst strata, field test and numerical simulation by FLAC^3D are carried out based on the Shuangbei tunnel in Chongqing. The field test shows that （1） secondary lining gradually bears load with the concrete hardening, and the axis force is always pressure, the arch vault is subjected to internal bending moment and the hance and side wall are subjected to external bending moments, the safety factor of arch vault is larger than that of side wall; （2） when the water pressure has great cyclo-hoop effect on the tunnel lining. The numerical simulation shows that （ 1 ） axial forces and bending moments increase linearly with the increasing of water pressure, both the axial force and the growth rat in the lower half section are higher than those in the upper half section obviously, bending moments growth rate shows as arch spring 〉 invert 〉 upper half section ; （3） when the drainage system capability is enough, the lined tunnel lining does not undertake water pressure, however, once the drainage system capability decreases, the anti-hydraulic performance of the lining is weak, and the arch spring and invert are the most unfavorable positions, which is most likely cause disasters of lining fracturing, water inrush and so on.